1. Field of the Invention
The present invention relates to a scanconverter system designed to convert an interlaced video signal to a non-interlaced video signal and equipped with a superimposing apparatus for forming desired image data by superimposing a computer-generated image on another image reproduced from a laser disc or the like.
2. Description of the Prior Art
There is known a superimposing apparatus which forms desired image data by superimposing a computer-generated image of characters, graphics and so forth on another image formed of video signals reproduced from a laser disc, video tape or the like. Generally in the apparatus of the type mentioned, video signals supplied from an external apparatus are first digitized and then are replaced partially with computer-generated image data to form interlaced superimposed image data.
In such conventional superimposing apparatus where interlaced superimposed image data is outputted, some problems are existent including a low image resolution and flicker on a display to consequently bring about difficulties in reading superimposed characters and so forth. For the purpose of solving the above problems, there is contrived a technique for processing the interlaced image data to form non-interlaced image data with the superimposition and outputting such non-interlaced image data.
In processing the interlaced image data to obtain non-interlaced image data, interpolation of scanning lines is performed by the use of a line memory unit or a frame memory unit, and a variety of devices have been proposed and developed for practical use to achieve the above purpose. However, if the interlaced superimposed image data outputted from such conventional superimposing apparatus is processed to form non-interlaced image data by merely using a line memory unit or a frame memory unit, there still remain some difficulties in sufficiently enhancing the image resolution and reducing the flicker without causing a visually unnatural impression.
When the interlaced superimposed image data outputted from the superimposing apparatus represents a still picture, satisfactory interpolation is attained by the use of a frame memory unit to produce non-interlaced image data. However, if a line memory unit is employed in such a case, it follows that the image data of a horizontal scanning line to be interpolated is composed of the data of the preceding horizontal scanning line, whereby vertical flicker is caused on a display screen to consequently deteriorate the vertical resolution. Accordingly, the computer-generated image data is not suited to form a non-interlaced one by the use of a line memory unit. When the interlaced superimposed image data outputted from the superimposing apparatus represents a moving picture, satisfactory interpolation can be executed by means of a line memory unit to form non-interlaced image data. However, if a frame memory unit is used for obtaining interlaced data, the image data of horizontal scanning line to be interpolated comes to be composed of the image data anterior by one or two fields, so that some visually unnatural impression is derived from the image displayed on the screen. Therefore, the image data thus formed of the moving-picture video signal is not suited for obtaining non-interlaced data by the use of a frame memory unit.